The collapsible ladder devices of the prior art were frequently encountered in wall mounted apparatus for use as a fire or emergency escape as typically illustrated in U.S. Pat. Nos. 350,047 and 3,756,347. A distinct limitation of those devices was that they were not designed for compact storage and more importantly, could not be readily transported for use elsewhere.
With regard to free standing collapsible ladders, the structures previously disclosed in the art generally included an arrangement of parallel rails with pivotally connected rungs such as described in U.S. Pat. Nos. 3,439,776, 3,722,622 and 2,875,935.
A distinct shortcoming of the foregoing ladders was that they did not provide self-storable capabilities. Although these previous devices incorporated rails that moved in parallelism, when the rails were in mutual contact with the ladder collapsed, one rail extended beyond the other, thus forming a longer mass. In addition, those devices of the prior art did not include an integrated latch arrangement for stabilizing the rungs in the unfolded mode or for securing the side rails when in the folded state.
The device of the present invention solves many of the problems of the prior art by providing an articulated ladder structure having the ability for compound pivotal and sliding movement. Although this general displacement application may have been shown in U.S. Pat. No. 2,972,153, the device of the instant invention, as will be apparent hereinafter, includes many components and structural features which improve upon and provide the degree of strength, durability and rigidity required for a load bearing ladder.